The present invention relates to rotary-wing aircraft such as helicopters. More specifically, the invention is directed to a system and a method for providing anti-torque and yaw control in a rotary-wing aircraft without the use of a conventional tail rotor.
Tail rotors are the most prevalent means for providing yaw control, and for overcoming the biasing torque generated by the main rotor in rotary-wing aircraft such as helicopters. Tail rotors, however, possess a number of substantial disadvantages. For example, tail rotors present a serious safety risk to ground personnel working in the vicinity of rotary-wing aircraft. In addition, inadvertent contact between tail rotors and stationary objects on the ground causes a substantial number of accidents each year. Tail rotors also necessitate the use of multiple bearings, right-angle gearboxes, and high-speed shafting, and thus raise reliability and maintainable issues.
Furthermore, small arms fire and projectiles from other types of weapons can incapacitate a tail rotor, leading to a sudden and total loss of anti-torque and yaw control and rendering the aircraft uncontrollable. This vulnerability is of particular concern in military aircraft. In addition, the tail rotor makes a substantial contribution to the overall acoustic signature of a rotary-wing aircraft, adds significantly to pilot workload, and can make a rotary-wing aircraft difficult to control in cross-wind conditions.
Tail rotors also possess substantial disadvantages from the standpoint of energy consumption. In particular, the power needed to operate a tail rotor usually represents a significant portion, e.g., fifteen percent, of a rotary-wing aircraft""s overall shaft-horsepower requirement. Thus, the use of a tail rotor necessitates a larger power plant than would otherwise be required, and increases the overall fuel consumption of the aircraft.
Systems that eliminate the need for a tail rotor have been developed. For example, U.S. Pat. Nos. 3,059,877; 4,200,252; and 4,948,068, each of which is incorporated by reference herein in its entirety, describe anti-torque and yaw-control systems based on the principle of circulation control (also referred to as circulation-control blowing). Circulation control is an aerodynamic phenomenon in which a bulk flow around a body is deflected by a sheet of air ejected tangentially to the surface of the body. The deflection of the bulk flow generates a force on the body in a direction opposite the deflected flow.
Circulation control in a rotary-wing aircraft is achieved using pressurized air from the aircraft""s engine, or an auxiliary fan mounted within the fuselage. The pressurized air is ejected from downwardly-facing slots in the right side of the aircraft""s aft fuselage, or tail boom. The resulting jets or sheets of air follow the contour of the tail boom, and deflect the downwash from the main rotor as it travels over the tail boom. This deflection produces a lateral force on the tail boom that partially counters the torque generated by the main rotor.
The systems disclosed in the above-noted patents, in general, do not produce sufficient force to fully counter the biasing torque of the main rotor. Thus, reaction jets are typically used to supplement the anti-torque force generated using circulation-control. More specifically, one or more jets of pressurized air are discharged in a lateral direction through nozzles mounted on the rearward portion of the tail boom. These jets produce a lateral force that counteracts the main rotor torque. The reaction jets also provide the yaw control previously furnished by the tail rotor. In particular, the reaction jets are capable of being throttled in response to pilot input. This feature permits the force produced by the jets (and, therefore, the net lateral force on the aircraft) to be varied, thereby facilitating yaw control.
Anti-torque and yaw-control systems based on circulation control permit a rotary-wing aircraft to be operated without most of the disadvantages associated with tail rotors. The reaction jets used in these systems, however, require a substantial amount of energy to operate. In fact, the energy requirements of reaction jets are roughly equivalent to those of a conventional tail rotor of comparable capabilities. Hence, aircraft that use circulation-control-techniques for anti-torque and yaw control, in general, require power-plants of approximately the same capacity and consume roughly equivalent amounts of fuel as comparable tail-rotor aircraft.
Reducing the overall power requirements of a rotary-wing aircraft can provide substantial benefits. For example, lowering the power requirements of an aircraft facilitates the use of smaller, lighter engines that consume lower amounts of fuel. These reductions can produce corresponding increases in the range and payload capacity of the aircraft. Alternatively, the power formerly dedicated to the tail rotor or jet thrusters can be used to drive a pusher fan located at the rear of the aircraft, thereby allowing the aircraft to achieve a higher maximum forward velocity than would otherwise be possible.
A preferred embodiment of a rotary-wing aircraft comprises a fuselage, a main rotor rotatably coupled to the fuselage and a tail boom fixedly coupled to the fuselage so that a least a portion of the tail boom is located within an area of downwash from the main rotor. The tail boom defines a plenum chamber therein for holding pressurized fluid.
A preferred embodiment also comprises a linear nozzle mounted on the tail boom and having an opening extending along the tail boom for discharging a sheet of fluid in a direction substantially tangential to an outer surface of the tail boom.
A preferred embodiment also comprises a yaw-control device defining an internal volume therein, wherein the yaw-control device is rotatably coupled to a lower portion of the tail boom and has a first and a second opening formed therein, the internal volume receives the pressurized fluid from the plenum chamber by way of the first opening, and the yaw-control device discharges the pressurized fluid from the internal volume and into the area of downwash from the main rotor by way of the second opening.
Another preferred embodiment of a rotary-wing aircraft comprises a main rotor, a tail boom extending through an area of downwash from the main rotor, and a linear nozzle fixedly coupled to the tail boom and having an opening extending along the tail boom for discharging a sheet of fluid in a direction substantially tangential to an outer surface of the tail boom. A preferred embodiment also comprises a yaw-control device movably coupled to the tail boom and having an opening formed therein for discharging fluid in a direction away from the yaw-control device and into the area of downwash from the main rotor.
A preferred embodiment of an anti-torque and yaw-control system for a rotary-wing aircraft having a main rotor and a tail boom located in an area of downwash from the main rotor comprises a linear nozzle for discharging a first jet of fluid in a direction substantially tangential to an outer surface of the tail boom to produce a layer of fluid flow that extends along the outer surface, and a yaw-control device for being movably coupled to the tail boom. The yaw-control device comprises an outer skin having an opening formed therein for discharging a fluid flow in a direction away from the yaw-control device.
Another preferred embodiment of a rotary-wing aircraft comprises a fuselage, a main rotor rotatably coupled to the fuselage, and a tail boom fixedly coupled to the fuselage so that a least a portion of the tail boom is located within an area of downwash from the main rotor.
A preferred embodiment also comprises a linear nozzle mounted on the tail boom and having an opening extending along the tail boom for discharging a sheet of the pressurized fluid in a direction substantially tangential to an outer surface of the tail boom and toward the yaw-control device.
A preferred embodiment also comprises a yaw-control device comprising an outer skin defining an internal volume within the yaw-control device for receiving the pressurized fluid. The outer skin has an opening formed therein for discharging the pressurized fluid from the internal volume in a direction away from the yaw-control device and into the area of downwash from the main rotor. The yaw-control device is rotatably coupled to the tail boom so that an orientation of the opening can be altered in relation to the tail boom thereby altering a circulation pattern of the rotor downwash around the tail boom.
A preferred method of counteracting main-rotor torque and controlling yaw in a helicopter having a main rotor and a tail boom located within an area of downwash from the main rotor comprises altering a direction of travel of the downwash from the main rotor by directing a first flow of fluid along an outer surface of the tail boom to produce a layer of fluid flow along at least a portion of the outer surface. A preferred method also comprises further altering the direction of travel of the downwash from the main rotor by using a movable yaw-control member to introduce a second flow of fluid into the area of downwash from the main rotor in a direction away from the yaw-control device.
Another preferred embodiment of a rotary-wing aircraft comprises a fuselage, a main rotor rotatably coupled to the fuselage, and a tail boom fixedly coupled to the fuselage so that a least a portion of the tail boom is located within an area of downwash from the main rotor. The tail boom defines a plenum chamber therein for holding pressurized fluid.
A preferred embodiment also comprises a linear nozzle mounted on the tail boom and having an opening extending along the tail boom for discharging a sheet of fluid in a direction substantially tangential to an outer surface of the tail boom, and a yaw-control device having a squared edge. The yaw-control device is coupled to a lower portion of the tail boom so that an opening is formed between the yaw-control device and the tail boom. The pressurized air from the plenum chamber is discharged through the opening. The yaw-control device is rotatable in relation to the tail boom so that a direction in which the pressurized air flows away from the yaw-control device is variable.